Porous wall structure



June 25, 1963 H. WHEELER, JR 3,095,283

' POROUS WALL STRUCTURE Filed June 22, 1959 3 Sheets-Sheet 1 INVENTOR.

HARRY L.WHEELE JR.

ATTORNEY June 25, 1963 H. L. WHEELER, JR

' POROUS WALL STRUCTURE 3 Sheets-Sheet 2 Filed June 22, 1 959 INVENTORHARRY L. WHEELER JR.

A TTDR NE).

June 25, 1963 H. L. WHEELER, JR

POROUS WALL STRUCTURE '3 Sheets-sheaf 3 Filed June 22, 1959 L J11 JDEVELOPMENT OF HELIX CIRCUMFERENCE or cYL= lit? 13 ff I15 INVENTOR.HARRY L. WHEELER JR.

AT TORNE Y United States Patent 3,095,283 POROUS WALL STRUCTURE Harry L.Wheeler, Jr., Madison Heights, Mich., assignor to The BendixCorporation, a corporation of Delaware Filed June 22, 1959, Ser. No.821,953 8 Claims. (Cl. 29191.6)

This invention relates to a porous wall structure and method of makingsame and more particularly to a porous Wall structure of the wire woundtype.

One of the objects of this invention is to provide a wire wound porouswall construction which is radially stronger than other known wire woundconstructions.

Another object of this invention is to provide a wire wound porous wallstructure and method of making same in which uniform pore spacing andsize may be more easily attained than in other comparable structures.

A further object of this invention is to provide a porous wall structureof helically wound wire forming a figure of revolution in which thenumber of pores and size of pores per unit area is constant and clearlydefinable regardless of the changing cross section of any figure ofrevolution.

A still further object of this invention is to provide a porous wallconstruction in the form of a figure of revolution such as, for example,a cylinder, a cone, or a vem turi shaped nozzle and which may further bereformed from such initial shapes into other asymmetrical forms or cutand reformed into flat sheets.

More specifically, it is an object of this invention to provide a wirewound porous wall structure which is fabricated by simultaneouslywinding a first wire having a smooth round surface and a second wirehaving a helicoidal surface about a mandrel in a side by siderelationship to form a figure of revolution having alternateconvolutions of said first and second wires arranged so that theconvolutions of one wire contact only the convolutions of the otherwire, and bonding said first and second wires to each other throughouttheir entire lengths at their points of contact to form uniforminterstices therebetween, said points of contact being spaced from eachother a distance equal to the pitch of the helices forming thehelicoidal surface on the second wire. Examples of wires having ahelicoidal surface are stranded wires, the strands of which are twistedto form helically disposed protuberances on the surface thereof, orsolid wires having a polygonal cross-section which are axially twistedto form helically disposed protuberances on the surface thereof.

Another object of this invention is to provide a wire wound porous wallstructure which can be machined without creating free ends or burrs.

A further object of this invention is to provide a wire wound porouswall structure and method of making same which will permit, on apractical basis, the forming of very large figures of revolution.

A still further object of this invention is to provide a wire woundporous wall structure which may be constructed at very low cost becauseof the rapid winding rate which may be used during fabrication.

Another object of this invention is to provide a wire wound porous wallstructure, made in accordance with this invention, which may be used for(l) fluid filters; (2) sweat or transpiration cooled surfaces such asrocket motors, nozzles, nose cones, turbine blades, afterburners,combustion chambers, and all structures subject to aerodynamic heating;(3) bearings; (4) reactor cores; (5) heat exchangers, and (6) otherapplications obvious to those skilled in the art.

Other objects and advantages of this invention will become apparent fromthe following description taken in connection with the accompanyingdrawings which form a part of this specification and in which:

FIGURE 1 is a perspective view of a porous wall cylinder constructed inaccordance with my invention;

FIGURE 1A is a fragmentary enlarged view of the circumscribed portion 1Ain FIGURE 1 which shows alternate convolutions of stranded and solidwires;

FIGURE 1B is a sectional view taken substantially along line 1B-1B ofFIGURE 1A;

FIGURE 2 is a fragmentary enlarged perspective view of a porous wallhaving two layers each of which includes three stranded wire and solidWire arranged and bonded in accordance with my invention;

FIGURE 3 is a fragmentary enlarged perspective view of a porous wall ofseven stranded wire and solid wire arranged and bonded in accordancewith my invention;

FIGURE 4 is a fragmentary enlarged perspective view of an alternatearrangement and construction of a porous wall having two or morelaminations;

FIGURE 5 is a fragmentary enlarged perspective view of a porous wallformed of wire having a smooth round surface and wire having a squarecross-section which has been axially twisted;

FIGURE 6 is a view partially in section of a porous wall cylinderconstructed in accordance with my invention which has a perforated coretherein;

FIGURE 7 is a perspective view of a porous wall cylinder constructed inaccordance with my invention which is partially broken away to show thefluted core therein;

FIGURE 8 is a side view of a wire having a square cross-section whichhas been axially twisted;

FIGURE 9 is a diagram showing the development of a helix;

FIGURE 10 is a diagrammatical view of a cone constructed in accordancewith my invention;

FIGURE 11 is a diagrammatical view showing a venturi nozzle and rocketmotor combustion chamber constructed in accordance with my invention;

FIGURE 12 illustrates diagrammatically in cross-section a turbine bladeconstructed in accordance with my invention; and

, FIGURE 13 is a diagrammatical view of an ellipsoid of revolution,minus the ends, constructed in accordance with my invention.

Referring to FIGURE 1, 1A and 1B it will be 'seen that the figure ofrevolution shown, namely the porous wall cylinder 12 of FIGURE 1,consists entirely of two different types of wires 14 and 16, the firstof which is a solid wire having a smooth round surface and the sec 0ndof which is a three stranded wire, the strands of which are helicallytwisted to form a helicoidal surface. The porous wall cylinder 12 isfabricated by winding under high tension the solid wire 14 and strandedwire 16 side by side about a cylindrical mandrel in such a manner thatthe convolutions of the solid wire contact only the convolutions of thestranded wire and vice versa.

The wire wound structure may then be placed in a furnace in a neutral orreducing atmosphere and heated to a temperature sufficient to bond thestranded wire and the solid wire to each other throughout their entirelengths at their points of contact to form a coherent porous cylinderhaving uniform porosity.

The preferred manner of fabricating a porous wall of the type discussedabove is to simultaneously wrap the two types of wire at a very lowpitch so that all of the wires on a single layer are in intimate side'by side contact. While it is simplest to wind one solid and oiiestranded wire simultaneously, it is also possible to wind two or moresolid and two or more stranded wires disposed alternately so that theend product will have the same appearance as though the wires were woundas a pair, except that the pitch will be higher.

If a wall thicker than that formed by one layer is required, a secondlayer having a construction identical to that of the first layer may beadded by starting at the same end of the mandrel from which the firstlayer was started. In making multiple layer walls it has been found verydesirable to use stranded and solid wires of dilferent effectivediameters, so that when the second layer is added a staggered nestingeffect is obtained, as shown in FIG- URE 1B. Any number of additionallayers may be added, each succeeding layer being wrapped in the samedirection and in the same manner as those preceding it. The nestingeffect obtained by the use of wires having different effective diametersnot only increases the axial strength of the finished structure, butalso may be used to control the tortuousity of the pores of intersticeswhich traverse the porous wall. In forming various porous wall structureof the type described, it has been found that where wires havingdifferent effective diameters are used, maximum packing densities andaxial strength may be achieved by utilizing wires having the followingdiametrical relationship:

Wherein Ds is the smaller diameter wire and De is the larger diameterwire.

If wires of equal effective diameter are used, the construction shown inFIGURE 4 may be obtained. However, nesting effects, as described withrespect to wires of unequal effective diameters, may also be obtained byusing stranded and solid wires of equal efi'ective diametens, if thewinding process is properly controlled. It should be pointed out that inthe FIGURE 4 embodimerit the pores traverse the wall in a somewhat moredirect manner than in the embodiment shown in FIG- URES 1B and 2. Theactual path followed by each pore of these embodiments is that of aspiral, the axis of which is curved and runs circumferentially about themandrel. It is important to note that, since a solid wire lies betweeneach stranded wire, the maximum pore opening is clearly and uniformlydefined by the stranded wire beaming against the solid wire. The size ofthis opening will be a function of the diameters of the individualstrands of the stranded wire and of the diameter of the solid wire.

Another method of wrapping which may be used in forming multiple layeredporous walls involves the use of a return stroke in applying the evennumbered layers during winding. However, if such a method is used, thewires will not nest as shown in FIGURES 1B and 2, and the structuretherefore will be weaker, more porous and more permeable.

The stranded wire used in connection with my invention may be composedof two or more strands which are helically twisted to in effect formhelically disposed protuberances on the surface of the stranded wire.The effective diameter of the wire will be determined by the size andnumber of strands used, and will be equal to the diameter of thesmallest circle circumscribing all of the strands in the wire. Groupingsof three and seven strands are most satisfactory because they producethe highest density packing. Note FIGURE 3 which shows a portion of aporous wall formed of a helically twisted seven stranded wire 18 l and asolid round wire 20.

The pitch with which the wires are twisted may be varied at will. Thus,the shorter the pitch, the greater the number of pores per unit lengthof wire, and the greater the radial inclination of the pore path.

Instead of using helically twisted stranded wire in the forming of thepreviously discussed porous structures, it is also possible to get asimilar effect by using a solid wire having a polygonal cross-sectionwhich has been helically twisted to form a helicoidal surface thereon.Thus, by winding a square wire 22, which has been twisted to formhelically disposed protuberances on the surface thereof, as shown inFIGURES 5 and 8, between solid round wires 24 in the manner previouslydescribed, predetermined uniform interstices or pores of the samegeneral nature as those formed when using comparable stranded wire willalso be formed in this instance. Instead of using solid round wires 24,solid square wires or other polygonal shaped wires might also be used inplace thereof. Helically twisted three stranded wire would have acomparable surface to that of a solid wire having a triangularcross-section which has been axially twisted, while helically twistedseven stranded wire would have a comparable surface to that of a solidwire having a hexagonal cross-section which has been axially twisted.The reason for the latter equivalency is that one of the strands of theseven stranded wire is in effect a core around which the other six wiresare helically disposed. It should be pointed out, however, that althoughthe pores formed between the solid round wire and the adjacent wirehaving the helicoidal surface are somewhat the same for equivalentwires, the stranded wires will have lower densities than their solidtwisted polygonal equivalents, and will of course be more porous.

The helices formed on the surface of both the twisted stranded wires andthe axially twisted polygonal shaped solid wire are true helices, thatis, each is a curve generated by a point moving about a cylindricalsurface (real or imaginary) at a constant rate in the direction of thecylinders axis. Referring to the diagram of FIGURE 9, it will be seenthat the lead of a helix is the distance that it advances in an axialdirection, in one complete turn about the cylindrical surface. If oneturn of a helical curve were unrolled onto a plane surface, as shown bythe diagram, the helix would become a straight line forming thehypotenuse of a right triangle. The length of one side of this trianglewould equal the circumference of the cylinder with which the helixcoincides, and the length of the other side of the triangle would equalthe lead of the helix. The angle A is often referred to as the helixangle and the angle B as the lead angle.

With this in mind, the square cross-section wire, shown in FIGURES 5 and8, which was axially twisted, could be referred to as a four lead helix,wherein the lead L is equal to four times the pitch P, the pitch beingthe axial distance from one helix to the next helix. The twisted threestrand wire or an axially twisted triangular crosssection wire could bereferred to as a three lead helix, wherein the lead is equal to threetimes the pitch.

After winding the wire having a helicoidal surface and the wire having asmooth round surface to the required wall thickness and in the desiredconfiguration in accordance with my invention, the figure of revolutionand mandrel may be placed in a furnace in a neutral or reducingatmosphere and heated to a temperature suificient to fuse or bond thetwo wires to each other throughout their entire lengths at their pointsof contact to form uniform interstices therebetween. Thus, bonding willoccur at these points of contact, said points being spaced from eachother a distance equal to the pitch of the helices formed on the surfaceof the wire having the helicoidal surface. it should also be noted thatwhere a stranded wire is utilized to form the structure, bonding willalso occur between the strands themselves.

The function of the overall bonding operation is to produce a porouswall capable of withstanding mechanical and hydraulic forces of itself,to prevent any shifting or gapping of the wires under the influence ofvibration or wedge shaped particles activated by hydraulic pressure, andto prevent the entire winding from disintegrating should one of thestrands become severed. The bonded porous structure will be completelyfree of any form of media migration, and will be resistant to potentialdamage resulting from fatigue or impact. Furthermore, the porousstructure may be ground or machined without the creation of any burrs.

Added strength may be gained if the wall is simultaneously bonded to themandrel, which may be a perforated core 26, as shown in FIGURE 6; or afluted core 28, as shown in FIGURE 7. Such arrangements, as shown inFIGURES 6 and 7 will permit flow of fluid therethrough and may be usedas effective filters.

After heating, the porous cylinder may be removed from the mandrel, ifthe mandrel is of ceramic or ceramic coated metal, and processed furtherby placing it between rollers in order to compact the porous structureand reduce the pore size. Such rolling, however, is not mandatory. Wherethe porous wall is not to be removed from the mandrel, it may still berolled. In this instance the mandrel will serve as one of the tworollers between which the porous wall is passed. Further bonding andstrengthening may be obtained if the porous structure is then given asecond heat treatment similar to the first. If desired, the porousfigure of revolution may be slit and rolled out into a fiat sheets.

The bonding of the individual wires may be accomplished by one or moreof the following means: (1) fusion at high temperature without thepresence of a liquid phase or any bonding agent; (2) by coating the wirewith a low melting point pure metal or alloy such as tin, silver,copper, gold, tin-lead alloys or copper-silver alloys, which wil meltand fuse or braze the structure into an integrated mass; (3) by sprayingor otherwise applying a finely divided form of brazing material (powder)between each layer of wrapping; (4) by spraying or otherwise applying aneasily reducible oxide such as, but not restricted to, CuO, CuO or AgOwhich will reduce to a low melting point metal in a reducing atmospherefurnace; (5) by wrapping in addition to the strand and solid wire athird very fine wire of brazing alloy; (6) by dipping the finishedwinding in a molten bath of tin, copper, plastic or other bondingmaterial.

The strength of the bonded joint is greatly increased by winding thewire under the highest possible tension so that a very firm contact isestablished between adjoining convolutions of wire.

The metal comprising the wire will be determined by the use for whichthe porous wall is intended. Thus, steel, copper, titanium, ormolybdenum wires, as well as alloys, to mention only a few, may beemployed to meet specific conditions. As a matter of fact my inventionmay be utilized in connection with plastic wires or wires of anymaterials which are connectible to each other by fusing, gluing or bysome other suitable means.

In the preferred embodiment which utilizes stranded wire and solid wirethe porosity or permeability will be controlled, as previouslydiscussed, by the size of the individual strands in the stranded wire,by the number of individual strands in the wire, by the pitch or twistof the strands, by the ratio of the efiective diameter of the strandedwire to the solid wire, and by the amount of rolling on the finishedstructure.

Some of the advantages of my invention are (1) the low cost ofconstruction due to the rapid winding rate which may be used; (2) thefact that there is virtually no limit to the diameter or length of theporous wall to be formed; (3) the fact that any shape of cylindrical ornear cylindrical cross-section can be made, such as the conical form 30of FIGURE 10, the rocket motor 32 of FIG- URE lil which has a nozzle 34,the ellipsoid of revolution 36 of FIGURE 13 which may be used fortorpedo shells, or missile and nose cone skins, and the turbine blade 38which may be pressed into the desired shape from a cylindrical figure ofrevolution; (4) the extremely uniform pore distribution which results inthe basic construction regardless of changing diameter; and (5) the factthat each wire in the structural wall is bonded to one or morecontiguous wires throughout its entire length.

The several practical advantages listed above which flow from myinvention are believed to be obvious from the previous description ofthe invention and other advantages and applications may suggestthemselves to those who are familiar with the art to which thisinvention relates.

Hlavingthus described the various features of my invention, what I claimas new and desire to secure by Letters Patent is: 1

l. A self-supporting porous wall structure capable independently ofother extraneous means of withstanding mechanical and hydraulic forcescomprising alternate contacting three stranded wires and solid wiresarranged so that each of said wires contacts only the other of saidwires, said stranded and solid wires being bonded to each :otherthroughout their entire lengths at their points of contact.

2. A self-supporting porous wall structure capable independently ofother extraneous means of withstanding mechanical and hydraulic forcescomprising a layer of alternate contacting first and second wiresarranged so that each of said wires contacts only the other of saidwires, one of said wires being a seven stranded wire the strands ofwhich are helically twisted to form helically disposed protuberances onthe surface thereof, said first and second wires being bonded to eachother throughout their entire lengths at predetermined points along saidhelically disposed protuberances to form non-variable intersticestherebetween.

3. A self-supporting porous wall structure forming a figure ofrevolution capable independently of other extraneous means ofwithstanding mechanical and hydraulic forces comprising a layer of[alternate contacting convolutions of first and second wires arranged sothat the convolutions of said first wire contact only the convolutionsof said second wire, one of said wires being a three stranded wire thestrands of which are helically twisted to form helically disposedprotuberances on the surface thereof, said first and second wires beingbonded to each other throughout their entire lengths at predeterminedpoints along said helically disposed protuberances to form uniformnon-variable interstices between said points.

4. A self-supporting porous .wall structure forming a figure ofrevolution capable independently of other extraneous means ofwithstanding mechanical and hydraulic forces comprising a layer ofalternate side by side contacting convolutions of a first round wire anda second seven stranded Wire having a helicoidal surface arranged sothat the convolutions of said first wire contact only the convolutionsof said second wire and the convolutions of said second wire con-tactonly the convolutions of said first wire, said first and second wiresbeing bonded to each other throughout their entire lengths at theirpoints of contact to form uniform non-variable interstices therebetween, said points of contact being spaced from each other a distanceequal to the pitch of the strands forming the helicoidal surface of saidsecond wire.

5. A self-supporting porous wall structure capable independently ofother extraneous means of withstanding mechanical and hydraulic forcescomprising a plurality of laminations each of which includes alternatecontacting three standed wires and solid wires arranged so that each ofsaid wires contacts only the other of said wires, said stranded andsolid wires being bonded to each other throughout their entire lengthsat their points of contact; said laminations being bonded to each otherat their points of contact to form a coherent porous laminar structure.

6. A porous wall structure as defined in claim 5 wherein the strandedwires of each of the laminations contact the solid Wires of the nextadjacent laminations while the solid Wires of each of said laminationscontact the stranded wires of said next adjacent laminations.

7. A porous wall structure as defined in claim 5 wherein the strandedwires of each of the laminations contact the stranded wires of the nextadjacent laminations while the solid wires of each of said laminationscontact the solid wires of said next adjacent laminations.

8. A self-supporting porous wall structure forming a figure ofrevolution capable independently of other extraneous means ofwithstanding mechanical and hydnaulic forces comprising a plurality oflaminations each of which includes alternate convolutions of contactingseven stranded Wires and solid wires arranged so that each of said Wirescontacts only the other of said wires, one of said wires having agreater effective diameter than the other of said wires, said strandedand solid wires being bonded to each other throughout their entirelengths at their points of contact; said laminations being arranged sothat the stranded wires of each of the laminations contact the solidwires of the next adjacent laminations while the solid wires of each ofsaid laminations contact the stranded wires of said next adjacentlaminations, said contacting wires being bonded to each other throughouttheir entire lengths at said points of contact to form a coherentlaminar structure.

References Cited in the file of this patent UNITED STATES PATENTSHurrel] Apr. 25, Liddell June 2, Johnson July 7, Kinnear Mar. 23, TurskyJan. 4, Layte Oct. 6, Specht July 13, Fernandez Mar. 19, Wheeler Oct.28,

FOREIGN PATENTS Germany Aug. 12,

1. A SELF-SUPPORTING POROUS WALL STRUCTURE CAPABLE INDEPENDENTLY OFOTHER EXTRANEOUS MEANS OF WITHSTANDING MECHANICAL AND HYDRAULIC FORCESCOMPRISING ALTERNATE CONTACTING THREE STRANDED WIRES AND SOLID WIRESARRANGED SO THAT EACH OF SAID WIRES CONTACTS ONLY THE OTHER OF SAID